CN118830036B

CN118830036B - Granulated powder for MnZn ferrite and method for producing the same, and MnZn ferrite and method for producing the same

Info

Publication number: CN118830036B
Application number: CN202380013893.0A
Authority: CN
Inventors: 吉田裕史; 藤枝崇周; 中村由纪子
Original assignee: JFE Chemical Corp
Current assignee: JFE Chemical Corp
Priority date: 2023-02-17
Filing date: 2023-10-12
Publication date: 2025-02-11
Anticipated expiration: 2043-10-12
Also published as: JPWO2024171517A1; CN118830036A; JP7450841B1

Abstract

The present invention provides a granulated powder capable of producing MnZn ferrite, wherein the MnZn ferrite has: regarding the M strength of a sintered body (model E42/15) of an E-type core in accordance with JIS C2560, the M strength has an excellent mechanical property of not only a high average value but also no samples with significantly low strength; and good magnetic properties with a loss value of less than 380kW/ ^m3 at 100°C, 100kHz and 200mT. In the granulated powder of the present invention, when the total of the iron compound, the zinc _compound and the manganese compound is calculated as 100 mol%, the iron compound is calculated as 51.5 to 56.8 mol% in terms of _Fe2O3 , _the zinc compound is calculated as 5.0 to 15.5 mol% in terms of ZnO, and the manganese compound is the balance in _terms of MnO, and the silicon compound is calculated as 50 to 300 mass ppm in terms of _SiO2 , the calcium compound is calculated as 100 to 1300 mass ppm in terms of CaO, and the niobium compound is calculated as 100 to 400 mass ppm in terms of _Nb2O5 relative to the total amount of the iron compound, the zinc compound _and the manganese compound, and the torque ratio of the granulated powder is 1.7 or more.

Description

Granulated powder for MnZn ferrite, method for producing same, and MnZn ferrite and method for producing same

Technical Field

The present invention relates to a MnZn ferrite and a granulated powder for the MnZn ferrite, which are particularly suitable for use in a magnetic core of an automobile-mounted component, and a method for producing the same.

Background

MnZn ferrite is a material widely used as a magnetic core of a noise filter, a transformer, and an antenna of a switching power supply or the like. Among soft magnetic materials, mnZn ferrite has a high magnetic permeability in kHz region, low loss, and lower cost than amorphous metals.

With recent hybrid and electrification of automobiles, mnZn ferrite used for a magnetic core of an electronic component for automobile mounting applications, which is in demand for expansion, is required to have a high breaking load. This is because MnZn ferrite is a ceramic and a brittle material, and is easily broken, and is continuously subjected to vibration in automotive applications and is continuously used in environments where it is easily broken, as compared with conventional household electrical appliance applications.

In case that ferrite having a low breaking load is mixed into a product, the automobile itself becomes inoperable with the breakage of the ferrite, and thus, prevention of the mixing of defective products having a low breaking load (occurrence of itself) is an important problem.

On the other hand, in the case of automobiles, it is also required to be light and space-saving, and therefore it is important to have good magnetic characteristics in addition to high breaking load as in the case of conventional applications.

As MnZn ferrite for automobile mounting applications in response to the above-described requirements, various developments have been made in the past, and if ferrite having good magnetic properties is mentioned, the inventions described in patent documents 1 and 2 are cited.

Further, as MnZn ferrite having improved mechanical properties in addition to magnetic properties, for example, the invention described in patent document 3 has been reported.

Prior art literature

Patent literature

Patent document 1, japanese patent application laid-open No. 2007-51052;

patent document 2, japanese patent application laid-open No. 2012-76983;

Patent document 3, japanese patent application No. 6730545.

Disclosure of Invention

Problems to be solved by the invention

However, although the techniques described in patent document 1 and patent document 2, for example, mention is made of a composition for achieving desired magnetic characteristics, the fracture toughness value is not described at all, and there is still a problem as a magnetic core of an electronic component for an automobile in-vehicle.

On the other hand, patent document 3 mentions improvement of mechanical properties in addition to magnetic properties, but only description of fracture toughness values as material properties is related to the mechanical properties. Here, the breaking load of the ferrite core is affected not only by the material characteristics but also by the properties of the breakage origin, and thus is affected by the stability of the manufacturing process and the product defects. That is, from the viewpoint of preventing occurrence of defective products with low breaking load and producing products of stable quality, it is not sufficient to control only the fracture toughness value.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a MnZn ferrite which has excellent mechanical properties such that a sintered body E42/15 having a long side of 42mm, a short side of 21mm, and a thickness of 15mm has M strength according to JIS C2560, of an E core body, and has a high average value and no appearance of a sample having significantly low strength, and a ring-shaped core body produced under the same conditions has good magnetic properties such that a loss value of 380kW/M ³ or less at 100 ℃ at 100kHz and 200mT, and a granulated powder for the MnZn ferrite, and a method for producing the granulated powder.

Solution for solving the problem

The inventors have conducted intensive studies to achieve the above object, and as a result, have obtained the following findings.

That is, the inventors have first found an optimum composition of Fe ₂O₃ and ZnO in MnZn ferrite capable of reducing the loss values of 100 ℃,100 kHz and 200 mT. If the composition is within this range, the magnetic anisotropy and magnetostriction are small, the resistivity is also maintained, and a secondary peak (secondary peak) which shows a minimum value of the temperature characteristic of the loss can also appear in the vicinity of 100 ℃, so that low losses of 100 ℃,100 kHz and 200mT can be achieved.

Further, it was found that by adding SiO ₂, caO, and Nb ₂O₅ in an appropriate amount as nonmagnetic components segregated in the grain boundaries, uniform grain boundaries can be formed, and the resistivity can be increased, thereby further reducing the loss value.

In addition, regarding the mechanical properties of MnZn ferrite, the following findings were also obtained as a result of examining the effective factors for improving the average value of M strength and not generating a sample having significantly low strength.

That is, the inventors have studied the cause of the decrease in M strength, focusing on the fact that a preexisting crack exists as a breakage origin at the center pillar root of the core. As the crack length becomes larger, the M strength tends to decrease. Then, the production process in which the pre-existing cracks were generated was examined, and as a result, it was found that the pre-existing cracks were already present when the granulated powder was pressed into a molded article.

Accordingly, as a result of focusing on the powder molding step, it was found that the propagation behavior of the molding pressure is different depending on the shape and surface properties of the molded granulated powder, and that the expansion rate at the time of demolding is different and cracking is likely to occur at the center pillar root of the core as the friction force is larger and the local molding density in the molded article is larger.

Next, a method capable of quantifying the amount of friction between granulated powders was examined. As a result, it was found that, when the fluidity of the powder was digitized into a torque using a powder rheometer capable of measuring the fluidity of the powder between a non-tapped and a 20-tap state as a state in which the bulk density of the powder was measured, when the value of the ratio (hereinafter, also referred to as "torque ratio") obtained by dividing the torque value in the non-tapped and smoothed state by the torque value after 20 taps was equal to or greater than a predetermined value, the granulated powder was small in friction and excellent in moldability, the local distribution of the molding density was suppressed, and the occurrence of cracks was suppressed.

The mechanism thereof can be presumed as follows.

Fig. 1 (a) shows a microscopic observation image of a granulated powder having a large friction force, in which a plurality of small cotton-like substances are adhered to the surface of the granulated powder (comparative example 3-1 described later), and fig. 1 (b) shows a microscopic observation image of a granulated powder having a small friction force, in which no cotton-like substances are adhered to the surface of the granulated powder and smoothed (inventive example 1-2 described later). In the state shown in fig. 1 (a), since the friction force between the granulated powders is large, the resistance to the rotational force of the blade of the powder rheometer becomes small after 20 times compaction, and the torque value of the blade of the powder rheometer is detected to be low. On the other hand, as shown in fig. 1 (b), when the surface of the granulated powder is smooth and the friction between the granulated powders is small, the torque value of the blade of the powder rheometer after 20 taps is detected to be high.

Therefore, the magnitude of the friction force on the surface of the granulated powder can be quantified in terms of the ratio of the torque values of the powder tackiness before and after the compaction operation, and by setting the numerical value to a predetermined value, occurrence of cracks in the molding step can be suppressed, and further, the average value of the M strength of the obtained sintered core is high, and occurrence of a core having a significantly low M strength can also be suppressed.

The present invention has been completed based on the above-described findings. That is, the main constitution of the present invention is as follows.

[1] A granulated powder for MnZn ferrite, which comprises an iron compound, a zinc compound, a manganese compound, a silicon compound, a calcium compound, a niobium compound and unavoidable impurities, wherein the total of the iron compound, the zinc compound, and the manganese compound is, in terms of Fe ₂O₃, znO, and MnO, 51.5 to 56.8mol% in terms of Fe ₂O₃, the zinc compound is, in terms of ZnO, 5.0 to 15.5mol% in terms of Mn, and the manganese compound is, in terms of MnO, the balance being, in terms of MnO, 50 to 300 mass ppm in terms of SiO ₂, 100 to 1300 mass ppm in terms of CaO, and 100 to 400 mass ppm in terms of Nb ₂O₅, based on the total amount of the iron compound, the zinc compound, and the manganese compound, and the granulated powder for MnZn ferrite, the torque ratio of which is 1.7 or more.

[2] The granulated powder for MnZn ferrite according to the above [1], wherein the granulated powder for MnZn ferrite further contains at least one of a cobalt compound and a nickel compound, the cobalt compound being 3500 mass ppm or less in terms of CoO and the nickel compound being 15000 mass ppm or less in terms of NiO, with respect to the total amount of the iron compound, the zinc compound and the manganese compound.

[3] A method for producing granulated powder for MnZn ferrite according to [1], which comprises a precalcining step of precalcining a mixture of an iron compound, a zinc compound and a manganese compound to obtain a precalcined powder, a mixing/pulverizing step of adding a silicon compound, a calcium compound and a niobium compound to the precalcined powder, mixing the same, and pulverizing the same to obtain a pulverized powder, a dipping step of dipping the pulverized powder in an alkali aqueous solution, and a granulating step of adding a binder to the pulverized powder after the dipping step, mixing the same, and granulating the same to obtain a granulated powder.

[4] A method for producing a granulated powder for MnZn ferrite according to [2] above, which comprises a precalcining step of precalcining a mixture of an iron compound, a zinc compound and a manganese compound to obtain a precalcined powder, a mixing/pulverizing step of adding at least one of a silicon compound, a calcium compound and a niobium compound to the precalcined powder, mixing the mixture with a cobalt compound and a nickel compound, and pulverizing the mixture to obtain a pulverized powder, an impregnation step of impregnating the pulverized powder with an aqueous alkali solution, and a granulating step of adding a binder to the pulverized powder after the impregnation step and mixing the mixture to obtain a granulated powder.

[5] A MnZn ferrite comprising a basic component, an auxiliary component and unavoidable impurities, wherein the basic component contains, in terms of Fe ₂O₃, znO and MnO, iron in an amount of 51.5 to 56.8mol% in terms of Fe ₂O₃, zinc in an amount of 5.0 to 15.5mol% in terms of ZnO, and manganese in the balance in terms of MnO, the auxiliary component contains, in terms of SiO ₂ in an amount of 50 to 300 mass ppm, caO in an amount of 100 to 1300 mass ppm, and Nb ₂O₅ in an amount of 100 to 400 mass ppm, and the minimum value of M strength measured on a sintered body of type E42/15 according to JIS C2560-3-1:2006, the number of samples being 100, exceeds 300N, and the average value is 600N or more.

[6] The MnZn ferrite according to [5], wherein the auxiliary component further contains at least one of CoO of 3500 mass ppm or less with respect to the basic component and NiO of 15000 mass ppm or less with respect to the basic component.

[7] The MnZn ferrite according to the above [5] or [6], wherein the MnZn ferrite has a loss value of 380kW/m ³ or less at 100 ℃, 100kHz and 200 mT.

[8] A method for producing a MnZn ferrite according to [5] comprises a precalcining step of precalcining a mixture of an iron compound, a zinc compound and a manganese compound to obtain a precalcined powder, a mixing/pulverizing step of adding a silicon compound, a calcium compound and a niobium compound to the precalcined powder and mixing them, pulverizing the mixture to obtain a pulverized powder, an impregnation step of impregnating the pulverized powder with an aqueous alkali solution, a granulating step of adding a binder to the pulverized powder after the impregnation step and mixing them, granulating the mixture to obtain a granulated powder, and a sintering step of molding the granulated powder to obtain a molded article, and sintering the molded article to obtain a MnZn ferrite.

[9] A method for producing a MnZn ferrite according to [6] comprises a precalcining step of precalcining a mixture of an iron compound, a zinc compound and a manganese compound to obtain a precalcined powder, a mixing/pulverizing step of adding a silicon compound, a calcium compound and a niobium compound to the precalcined powder, and further adding at least one of a cobalt compound and a nickel compound to the mixture, mixing the mixture, pulverizing the mixture to obtain a pulverized powder, an impregnating step of impregnating the pulverized powder with an aqueous alkali solution, a granulating step of adding a binder to the pulverized powder after the impregnating step, mixing the mixture, granulating the mixture to obtain a granulated powder, and a sintering step of molding the granulated powder to obtain a molded article, and sintering the molded article to obtain a MnZn ferrite.

Effects of the invention

According to the present invention, there can be provided a MnZn ferrite which has excellent mechanical properties such that the M strength of a sintered body E42/15 having a long side of 42mm, a short side of 21mm, and a thickness of 15mm according to JIS C2560 regarding an E core is high, and that a sample having a remarkably low strength does not appear, and also has excellent magnetic properties such that the loss value of a toroidal core manufactured under the same conditions is 380kW/M ³ or less at 100 ℃ at 100 kHz.

Drawings

FIG. 1 (a) is a microscopic observation image of a granulated powder having a large friction force, in which a plurality of small cotton-like objects are adhered to the surface of the granulated powder (comparative example 3-1). Fig. 1 b is a microscopic observation image of a granulated powder (invention examples 1 to 2) having a small friction force, which was smoothed without cotton adhering to the surface of the granulated powder.

Detailed Description

In general, in order to reduce the loss value of MnZn ferrite, it is effective to reduce magnetic anisotropy and magnetostriction. In order to achieve this, the blending amount of Fe ₂O₃, znO, and MnO, which are main components of the MnZn ferrite, needs to be selected from an appropriate range. In addition, by applying sufficient heat in the sintering step of the MnZn ferrite, crystal grains in the ferrite are moderately grown, and movement of domain walls (magnetic domain wall) in the crystal grains in the magnetizing step can be facilitated. Further, in the present invention, by adding a component that segregates at the grain boundaries, a grain boundary of a moderate and uniform thickness is generated, whereby the resistivity is maintained and the eddy current loss is reduced, thereby realizing low loss in the region of 100 to 500 khz.

In addition to the above magnetic characteristics, the magnetic core of an electronic component for use in an automobile is required to have a stable and high breaking load, and is not broken even in an environment in which vibration is continuously applied. This is because, when the MnZn ferrite as the magnetic core is broken, the inductance is greatly reduced, and the electronic component cannot exhibit a desired function. Therefore, the entire automobile may not be operated.

Therefore, mnZn ferrite used for electronic components for automobile use is required to have both magnetic characteristics such as low loss and a high and stable breaking load value.

Embodiments of the present invention will be further described below. The present invention is not limited to the following embodiments. In the present specification, the numerical range indicated by "-" includes numerical values described before and after "-" as a lower limit value and an upper limit value, respectively.

In the present invention, the composition of the MnZn ferrite is defined. First, the reason why the composition of MnZn ferrite (hereinafter, also simply referred to as ferrite) is limited to the following range in the present invention will be described. The iron, zinc, and manganese contained in the present invention as basic components are expressed as values converted into Fe ₂O₃, znO, and MnO, respectively. The contents of Fe ₂O₃, znO, and MnO are expressed as mol% when the total amount of iron, zinc, and manganese converted to Fe ₂O₃, znO, and MnO is 100 mol%. Further, the content of the auxiliary component and the unavoidable impurities is expressed in mass ppm relative to the above-mentioned basic component.

The basic components will be described below.

Fe₂O₃:51.5~56.8mol%

In the basic component, when Fe ₂O₃ is smaller or larger than the proper amount range, the magnetic anisotropy is large and the magnetostriction is also large, which leads to an increase in loss. Therefore, the content of Fe ₂O₃ is 51.5mol% or more and 56.8mol% or less. The content of Fe ₂O₃ is preferably 56.7mol% or less.

ZnO:5.0~15.5mol%

When ZnO is less than the proper range, the curie temperature becomes too high, so the loss value of 100 ℃ increases. Therefore, znO is contained at least at 5.0 mol%. The ZnO content is preferably 5.5mol% or more. On the other hand, when the ZnO content is more than the proper range, the loss value of 100 ℃ increases because the sub-peak temperature at which the loss value shows a minimum value decreases. Therefore, the upper limit of the ZnO content is 15.5mol%. The ZnO content is preferably 15.0mol% or less.

MnO balance

In the present invention, the balance of the basic component of the MnZn ferrite is MnO. This is because if the remaining amount is not MnO, the loss value under excitation conditions of 100 ℃, 100kHz, 200mT is not 380kW/m ³ or less. The content of MnO is preferably 30.0mol% or more, more preferably 30.5mol% or more. The content of MnO is preferably 43.0mol% or less, more preferably 42.0mol% or less.

The basic components are described above, and the auxiliary components are as follows.

50-300 Mass ppm of SiO ₂

SiO ₂ is known to contribute to the homogenization of the crystal structure of ferrite, and by adding SiO ₂ in an appropriate amount, abnormal grain growth can be suppressed and the resistivity can be improved. Further, with the addition of an appropriate amount of SiO ₂, the loss value under excitation conditions of 100 ℃, 100kHz, and 200mT can be reduced. Therefore, siO ₂ is contained at a minimum of 50 mass ppm. On the other hand, when the content of SiO ₂ is too large, abnormal crystal grains appear, and the loss value is significantly deteriorated, so that the content of SiO ₂ is 300 mass ppm or less. The content of SiO ₂ is preferably 55 mass ppm or more, more preferably 60 mass ppm or more. The content of SiO ₂ is preferably 275 mass ppm or less, more preferably 250 mass ppm or less.

100-1300 Mass ppm of CaO

Cao has an effect of segregation at grain boundaries of MnZn ferrite and suppressing grain growth, and by adding an appropriate amount of Cao, the resistivity can be increased, and loss values under excitation conditions of 100 ℃,100 kHz, and 200mT can be suppressed. Therefore, caO is contained at least in an amount of 100 mass ppm. On the other hand, when the CaO content is too large, abnormal grains are generated and the loss value is deteriorated, so that the CaO content is 1300 mass ppm or less. The CaO content is preferably 120 mass ppm or more, more preferably 150 mass ppm or more, and still more preferably 200 mass ppm or more. The CaO content is preferably 1200 mass ppm or less, more preferably 1100 mass ppm or less.

Nb ₂O₅ -400 mass ppm

Nb ₂O₅ is known to have effects of segregation at grain boundaries of MnZn ferrite, gradually suppressing grain growth, and relaxing stress between grain boundaries caused by grain growth. Accordingly, by adding Nb ₂O₅ in an appropriate amount, the loss value can be reduced, and thus Nb ₂O₅ is contained at a minimum of 100 mass ppm. On the other hand, when the content of Nb ₂O₅ is too large, abnormal crystal grains appear, and the loss value is remarkably deteriorated, so that the content of Nb ₂O₅ is 400 mass ppm or less. The content of Nb ₂O₅ is preferably 120 mass ppm or more, more preferably 130 mass ppm or more. The content of Nb ₂O₅ is preferably 380 mass ppm or less, more preferably 375 mass ppm or less, and still more preferably 350 mass ppm or less.

The MnZn ferrite of the present invention may further contain the following additives as auxiliary components.

CoO 3500 mass ppm or less

CoO is a component containing Co ²⁺ ions having positive magnetic anisotropy, and by adding this component, the temperature width of the minor peak of the minimum temperature showing loss can be widened. The lower limit of the CoO content is not particularly limited and may be 0 mass ppm, but in order to obtain this effect, it is preferable to add more than 500 mass ppm. On the other hand, when the CoO content is 3500 mass ppm or less, negative magnetic anisotropy of other components can be canceled, and the initial permeability can be prevented from decreasing. More preferably, the CoO content is 2500 mass ppm or less.

NiO of 15000 mass ppm or less

NiO selectively enters the B site of spinel crystal lattice, so that the Curie temperature of the material is improved, the saturation magnetic flux density is improved, and the loss value is reduced. The lower limit of the content of NiO is not particularly limited and may be 0 mass ppm, but in order to obtain this effect, it is preferable to add 1200 mass ppm or more, and more preferably 1500 mass ppm or more. More preferably 2000 mass ppm or more. On the other hand, by setting the NiO content to 15000 mass ppm or less, the magnetostriction can be further prevented from increasing, and the loss value can be further prevented from decreasing. Therefore, when NiO is added, the content of NiO is preferably 15000 mass ppm or less. More preferably 12000 mass ppm or less.

Unavoidable impurities

The MnZn ferrite of the present invention contains unavoidable impurities such as phosphorus, boron, chlorine, etc., but it is preferable to suppress them to several hundred mass ppm or less.

The ferrite granulated powder of the present invention contains an iron compound, a zinc compound, a manganese compound, a silicon compound, a calcium compound, a niobium compound, and unavoidable impurities. Further, at least one of a nickel compound and a cobalt compound may be contained as necessary.

The total amount of the iron compound, the zinc compound, and the manganese compound is 51.5 to 56.8mol% in terms of Fe ₂O₃, 5.0 to 15.5mol% in terms of ZnO, and the manganese compound is the balance in terms of MnO, based on 100mol% in terms of Fe ₂O₃, znO, and MnO.

The silicon compound is 50 to 300 mass ppm in terms of SiO ₂, the calcium compound is 100 to 1300 mass ppm in terms of CaO, and the niobium compound is 100 to 400 mass ppm in terms of Nb ₂O₅, relative to the total amount of the iron compound, the zinc compound, and the manganese compound. The cobalt compound is 3500 mass ppm or less in terms of CoO, and the nickel compound is 15000 mass ppm or less in terms of NiO.

The reason for limiting the content of each component is the same as the reason described in the explanation of each component of the ferrite.

In the present invention, the ratio (torque ratio) of the dynamic flowability (torque value) after 20 times of compaction to the dynamic flowability (torque value) at the time of non-compacted bulk density filling, as measured by using a powder rheometer, needs to be 1.7 or more with respect to the granulated powder obtained in the production process described later. As described above, when the torque ratio is 1.7 or more, the granulated powder has small friction and excellent moldability, and can suppress local distribution of molding density and occurrence of cracks. The upper limit of the torque ratio is not particularly limited, and in the granulated powder of the invention, the torque ratio is approximately 2.50 or less.

The mechanism related to the decrease in the torque ratio and the core strength is considered as follows. That is, in the MnZn ferrite, in the production process, the powder is produced and then subjected to the powder compacting treatment, but in this case, if the friction between the powders is large, the pressure from the pressing of the die is attenuated by the friction between the granulated powders. In addition, the action of rearrangement of the granulated powder to the gaps between the granulated powders in order to release the pressure is less likely to occur. As a result, the obtained molded article has a local variation in density distribution, and the expansion ratio of the molded article at the time of demolding also varies. In particular, when the variation in the expansion ratio is too large, the molded article becomes unable to maintain a desired shape, and cracks are generated. Since the cracks remain after sintering the molded article, the strength of the ferrite core obtained by the sintering is induced to decrease.

In contrast, in the present invention, it is important to perform the impregnation treatment of immersing the pulverized powder in an aqueous alkali solution. The impregnation treatment is a treatment of imparting hydroxyl groups to the surface of the pulverized powder, which hydroxyl groups can improve the adhesion between the organic binder added to the granulated powder and the pulverized powder constituting the granulated powder, and the shape retention of the binder becomes strong. Accordingly, the amount of the pulverized powder as primary particles which is detached from the granulated powder is reduced, and finally the granulated powder having a smooth surface is obtained (refer to fig. 1 (b)).

The aqueous alkali solution can be selected from aqueous ammonia, aqueous ammonium carbonate solution, aqueous ammonium bicarbonate solution, and the like. The aqueous alkali preferably has a solute concentration of 0.01mol/L or more, and more preferably has a solute concentration of 0.1mol/L or more. The upper limit of the solute concentration of the aqueous alkali solution is not particularly limited, and the solute concentration may be 5.0mol/L or less. The amount of the aqueous alkali solution is preferably 0.20 or more, more preferably 0.50 or more, as the amount of the aqueous alkali solution divided by the mass of the pulverized powder. The upper limit of the value is not particularly limited, and the value may be 1.50 or less. The time of the dipping treatment is not particularly limited, but is preferably 5 minutes or more and can be 120 minutes or less.

If only the smoothness of the surface of the granulated powder is considered, the composition of the aqueous alkali solution is not different in effectiveness even if it contains a metal component and a phosphoric acid component. However, the metal component is not decomposed and scattered as in the case of the non-metal component in the subsequent sintering step, and remains. This residual metal component reacts with the component constituting the MnZn ferrite, and affects grain growth, thereby preventing realization of desired magnetic characteristics. In addition, the same applies to the phosphoric acid component, and in particular, the phosphorus component induces abnormal grain growth, so that not only the desired magnetic properties cannot be obtained after the sintering step, but also the strength of the core is significantly impaired. Therefore, the components of the aqueous alkali solution preferably contain a nonmetallic component and do not contain a metallic component and a phosphoric acid component.

After the impregnation treatment in the aqueous alkali solution, the pulverized powder is separated from the aqueous alkali solution by a step such as filtration and recovered. The recovered crushed powder can be directly sent to the next process, or can be dried and then sent to the next process. The obtained immersed pulverized powder is slurried with water and a known organic binder such as polyvinyl alcohol, and then granulated by a spray drying method or the like.

In addition, as a secondary effect of reducing the friction force of the granulated powder, stabilization of the filling weight into the mold at the time of molding is exemplified. Particularly, when the filling speed into the mold is increased, the filling weight of the granulated powder into the mold tends to become unstable, and the weight of the obtained product core tends to vary for each sample. By reducing friction between the granulated powders, weight variation of each of the samples can be suppressed.

In addition, not only the composition, but also various characteristics of MnZn-based ferrite are greatly affected by various parameters. The MnZn ferrite of the present invention is also provided with the following definitions for obtaining magnetic properties and mechanical properties.

That is, in the MnZn ferrite of the present invention, the minimum value of M strength measured on 100 samples of sintered bodies of type E42/15 (sintered bodies of long side: 42mm, short side: 21mm, and thickness: 15 mm) according to JIS C2560-3-1:2006 is more than 300N, and the average value is 600N or more. The MnZn ferrite as a ceramic is a brittle material, and not only magnetic characteristics but also strength are specified in JIS C2560. In particular, in vehicle-mounted applications, since the vehicle-mounted applications are often used in environments where vibration is applied, a method for manufacturing a high-strength product that does not break even when subjected to impact and does not produce a low-strength product is required. In the present invention, by satisfying the above-described composition and the conditions of the granulated powder, the produced core can effectively suppress cracking that becomes the starting point at the time of breakage, the average strength at the time of measuring the M strength of 100 samples is 600N or more, and the minimum value of the M strength exceeds 300N, that is, a low-strength core having the M strength of 300N or less does not appear, and a core having stable strength characteristics can be obtained.

Next, a method for producing the MnZn ferrite of the present invention will be described. The method for producing a MnZn ferrite comprises a precalcination step of precalcining a mixture of the basic components and cooling the mixture to obtain a precalcined powder, a mixing/pulverizing step of adding the auxiliary components to the precalcined powder and mixing the same, and pulverizing the same to obtain a pulverized powder, an impregnation step of impregnating the pulverized powder with an aqueous alkali solution, a granulation step of adding a binder to the pulverized powder impregnated with the aqueous alkali solution and mixing the same, and granulating the same to obtain a granulated powder, a molding step of molding the granulated powder to obtain a molded body, and a sintering step of sintering the molded body to obtain a MnZn ferrite.

In the production of MnZn ferrite, first, fe ₂O₃, znO, and MnO powders as basic components are weighed so as to be the above-described ratios, and these are sufficiently mixed to prepare a mixture, and then the mixture is subjected to pre-calcination, and cooled to prepare a pre-calcined powder (pre-calcination step).

To the thus obtained precalcined powder, the auxiliary components specified in the present invention are added at a specified ratio and mixed, followed by pulverization (mixing-pulverizing step). In this step, the powder is sufficiently homogenized without variation in the concentration of the added component, and the pre-calcined powder is finely divided to a target average particle size (1.0 to 1.5 μm) to prepare a pulverized powder.

Subsequently, the obtained pulverized powder is immersed in an aqueous alkali solution, whereby surface modification is performed (immersing step). This step is considered to function to impart hydroxyl groups to the surface of the pulverized powder. The hydroxyl group thus added has an effect of improving the adhesion with the binder added at the time of granulation as a next step. Therefore, the granulated powder obtained in this way has a smooth surface and a small friction between the granulated powders, is excellent in filling property during molding, and is easy to promote rearrangement of the granulated powder at the time of pressurization, and is less likely to cause a difference in density distribution at each position in the mold, so that cracking of the molded article generated at the time of mold release can be suppressed in particular. Therefore, the effect of suppressing the strength failure of the finally obtained core product can be obtained.

The immersed pulverized powder is filtered to remove an alkali aqueous solution, and then a known organic binder such as polyvinyl alcohol is added thereto, followed by granulation by a spray drying method or the like, to obtain a granulated powder (granulation step). In this case, the obtained granulated powder satisfies the conditions within the above-mentioned numerical range with respect to the dynamic flowability at the time of filling to the bulk density and after 20 times of tapping.

Thereafter, the granulated powder is subjected to a step of sieving for adjusting the particle size, etc., as needed, and is molded by applying pressure with a molding machine to obtain a molded article (molding step). Next, the molded body is sintered under known sintering conditions to obtain the MnZn ferrite of the present invention (sintering step).

The MnZn ferrite can be suitably subjected to surface polishing or other processing.

The MnZn ferrite thus obtained has excellent mechanical properties which are not possible with conventional MnZn ferrites, that is, the M strength of the sintered body E42/15 having a long side of 42mm, a short side of 21mm, and a thickness of 15mm measured in accordance with JIS C2560, as measured in relation to an E-type magnetic core, is as high as 600N or more on average, and does not exhibit a specimen having a significantly low M strength of 300N or less. Further, good magnetic characteristics were simultaneously achieved such that the loss values of 100 ℃,100 kHz, and 200mT of the toroidal core manufactured under the same conditions were 380kW/m ³ or less.

The loss values of the toroidal core were measured at 100kHz and 200mT using a core loss measuring device (rock-through measurement: SY-8232) after performing primary side 5 turns and secondary side 5 turns on the core.

Further, regarding the strength of the sintered core, M strength of the sintered body E42/15 having a long side of 42mm, a short side of 21mm and a thickness of 15mm was measured according to JIS C2560-3-1 (2006), 100 samples were measured for each standard, and the average value of the calculated values and the number of samples of 300N or less were measured.

The method for producing the sintered body (MnZn ferrite) not described in the present specification is not particularly limited in terms of its conditions, equipment used, and the like, and may be a so-called conventional method.

Examples

Example 1

When Fe contained was converted to Fe ₂O₃, zn contained was converted to ZnO, and Mn contained was converted to MnO, each raw material powder weighed so that Fe ₂O₃, znO, and MnO were in the ratios shown in table 1 was mixed for 16 hours by a ball mill, and then pre-calcined in the atmosphere at 900 ℃ for 3 hours, and cooled to room temperature in the atmosphere for 1.5 hours, to prepare a pre-calcined powder.

SiO ₂, caO and Nb ₂O₅ corresponding to 150, 700 and 250 mass ppm, respectively, were weighed and added to the pre-calcined powder, and mixed-pulverized with a ball mill for 12 hours to obtain pulverized powder.

Next, the pulverized powder was immersed in ammonia water at a mass ratio of 0.6 to the pulverized powder for 1 hour using ammonia water at a concentration of 0.1mol/L, the ammonia water was removed by filtration or the like, water and polyvinyl alcohol were added to make a slurry, and the slurry was spray-dried to granulate. The particle size of the sample of the granulated powder was substantially the same as in the examples and comparative examples by sieving. The composition of the granulated powder was the same as that of the ferrite obtained.

The granulated powder thus obtained was quantified for fluidity by the rotational torque value of the blade in both a loose bulk density state in which the powder was filled with only non-tap and a state in which the powder was tap-pressed 20 times under the following conditions. The ratio (torque ratio) of the torque value after 20 taps divided by the torque value in the state of filling only the non-tap was obtained. The results are shown in Table 1.

Then, a pressure of 118MPa was applied to the granulated powder to obtain a molded body having an annular shape and an E-shape. These molded bodies were then charged into a sintering furnace and sintered in a gas flow of nitrogen and air mixed at a maximum temperature of 1320 ℃ for 2 hours to obtain a sintered body annular-shaped core body (n=3) having an outer diameter of 25mm, an inner diameter of 15mm and a height of 5mm and a sintered body E-shaped (E42/15) core body (n=100) having a long side of 42mm, a short side of 21mm and a thickness of 15 mm. The E-shaped core was molded at a molding stroke of 15 pieces/min, and the sintered core had a target weight of 45.0g.

Method for measuring Torque

A loose bulk density was obtained by allowing a sample of 44g (the height corresponds to about 51mm in the case of performing the inverse operation) to naturally fall down in a cylindrical glass container having an inner diameter of 25mm and a volume of 25 mL.

Tap Density the procedure of naturally dropping the sample filled to a loose bulk Density from a height of 4cm was repeated 20 times (tap 20 times).

Measurement apparatus A powder rheometer FT4 (blade rotation speed: 100mm/s, blade diameter: 23.5 mm) manufactured by Fu Ruiman technology Co was used.

Torque measurement, for loose bulk density and tap density, the blade of FT4 was rotated and lowered to a predetermined height and then lifted to a predetermined height 7 times in succession. Torque was calculated from the flow energy of the 7 th time. Further, a torque ratio is calculated from the torque for loose bulk density and the torque for tap density.

The loss value of the toroidal core was obtained by the above method, and the average strength at 100 samples (total number inspection) and the occurrence rate of cores of 300N or less were obtained from the M strength of the E-type (E42/15) core according to JIS C2560 using an Autograph. The results obtained are shown in Table 1. In addition, of all the standard samples, the samples with n=100 were all in the range of 45.0g±3% with respect to the weight of the E-shaped core after sintering.

TABLE 1

As shown in table 1, in any of the standard samples according to the present invention, the surface of the granulated powder was smoothed by immersing the pulverized powder in an aqueous alkali solution, whereby molding failure was suppressed, and the average M strength and the occurrence rate of cores having significantly low M strength were each shown to be preferable values. Further, in the invention examples 1-1 to 1-5, the loss values of 100℃100kHz 200mT were 380kW/m ³ or less when the magnetic properties were observed. Therefore, it is found that the inventive examples have both the high strength and the suitable magnetic properties.

In contrast, in the comparative examples (comparative examples 1 to 1) containing less than 51.5mol% of Fe ₂O₃ and the comparative examples (comparative examples 1 to 2) containing more than 56.8mol% of Fe ₂O₃, although high toughness can be achieved, the magnetic anisotropy and magnetostriction become large, and thus the loss value increases, and the loss value at 100℃and 100kHz and 200mT does not satisfy 380kW/m ³ or less. In contrast, in the comparative examples (comparative examples 1 to 4) containing ZnO in an amount larger than the range of the present invention, the secondary peak of the loss display minimum value was reduced, and in the above comparative examples, the loss values at 100 ℃.

Example 2

When Fe contained was converted to Fe ₂O₃, zn contained was converted to ZnO, and Mn contained was converted to MnO, raw materials were weighed so that the compositions of Fe ₂O₃:53.0 mol%, zno:12.0mol% and mno:35.0mol% (the same as in inventive examples 1-2 of example 1) were mixed for 16 hours by using a ball mill, and then pre-calcined at 900 ℃ for 3 hours in the atmosphere, and cooled to room temperature over 1.5 hours in the atmosphere, to obtain a pre-calcined powder.

To the pre-calcined powder, siO ₂, caO, and Nb ₂O₅ in the amounts shown in table 2 below were added, coO or NiO was added to a part of the samples, and mixing-pulverization was performed for 12 hours by a ball mill, to obtain pulverized powder.

The ratio (torque ratio) of the torque value after 20 times of compaction divided by the torque value in the state of filling only the non-compacted state was obtained for the granulated powder thus obtained using a powder rheometer in the same manner as in example 1. The results are shown in Table 2.

For each of these samples, the characteristics were evaluated by the same method and apparatus as in example 1. The results obtained are shown in Table 2. In addition, among all the standard samples shown in table 2, the samples with n=100 were all in the range of 45.0g±3% with respect to the weight of the E-shaped core after sintering.

TABLE 2

As shown in table 2, in any of the standard samples according to the present invention, the surface of the granulated powder was smoothed by immersing the pulverized powder in an aqueous alkali solution, whereby molding failure was suppressed, and the average M strength and the occurrence rate of cores having significantly low M strength were each shown to be preferable values. Further, when the magnetic properties are focused, in invention examples 2-1 to 2-11 in which the amounts of SiO ₂、CaO、Nb₂O₅, coO and NiO are within the scope of the present invention, the loss values of 100℃100kHz and 200mT are 380kW/m ³ or less. Therefore, it is found that the inventive examples have both the high strength and the suitable magnetic properties.

In contrast, in comparative examples 2-1, 2-3 and 2-5, in which only one of three components of SiO ₂, caO and Nb ₂O₅ was included in a range smaller than the range of the present invention, it was found that the grain boundary formation became insufficient, and therefore the resistivity was lowered, and the loss value was deteriorated due to the increase in eddy current loss. Further, it was found that in comparative examples 2-2, 2-4 and 2-6 in which only one of the above three components was excessive, the loss value was deteriorated due to the occurrence of abnormal crystal grains, and the mechanical properties were also greatly deteriorated.

Example 3

Raw materials were weighed, mixed and pulverized by the method shown in example 1 so that the basic components and the auxiliary components had the same composition as in inventive examples 1-2, to prepare pulverized powders.

Standard samples were prepared by immersing the pulverized powder in an aqueous alkali solution under the conditions shown in table 3, and standard samples were prepared without the treatment.

Adding polyvinyl alcohol into the treated or untreated crushed powder, and performing spray drying granulation. The particle size of the sample of the granulated powder was substantially the same as in the examples and comparative examples by sieving. The composition of the granulated powder was the same as that of the ferrite obtained.

The torque values of the granulated powders thus obtained were measured by the same method as in example 1 using a powder rheometer, and the torque ratios were obtained. The results are shown in Table 3.

For each of these samples, the characteristics were evaluated by the same method and apparatus as in example 1. Further, regarding the weight of the E-shaped core after sintering, all samples of n=100 were measured, and numbers outside the range of 45.0g±3% were recorded. The results obtained are shown in Table 3.

TABLE 3

In invention examples 1-2, 2-7, 2-10 and 3-1 to 3-5 satisfying the regulations of the present invention, the ratio (torque ratio) of the torque value obtained by compacting 20 times divided by the torque value in the non-vibration state is as high as 1.7 or more, and a smooth granulated powder is obtained, so that occurrence of cracks in the molded article can be suppressed. As a result, as for the M intensity, it was found that the average value was high and no sample with significantly low intensity was present. Further, since friction between the granulated powders can be reduced, the filling weight at the time of filling the granulated powders into the mold is stable, and therefore, even under the condition that the molding stroke is as fast as 15 pieces/min, a sample having a large weight deviation does not occur.

On the other hand, in comparative example 3-1 in which the treatment of immersing the pulverized powder in the aqueous alkali was not performed, since the adhesion of the binder to the primary particles was not enhanced, the surface smoothness of the granulated powder was poor, and therefore the value of the ratio obtained by dividing the torque value after compaction 20 times by the torque value in the non-vibrating state was as low as less than 1.7. Therefore, cracks easily occur in the molded article, and samples having low average M strength and significantly low M strength of the obtained core appear. Further, due to the influence of the increase in friction between the granulated powders, the mold filling amount at the time of molding was unstable, and samples out of the target range of 45.0g±3% were present when the weight was measured in the state of the sintered core.

The bulk density of the non-tapped bulk density of the invention examples 1-2 was 1.40g/cm ³, and the bulk density after 20 taps was 1.48g/cm ³. In contrast, the bulk density of the comparative example 3-1 was 1.38g/cm ³, and the bulk density after 20 taps was 1.44g/cm ³. Therefore, the tap densities of the invention examples 1-2 and the comparative examples 3-1 were almost the same.

Industrial applicability

As described above, the MnZn ferrite defined in the present invention has both good magnetic properties such that the loss value under excitation conditions of 100 ℃ 100kHz and 200mT is 380kW/M ³ or less, and excellent mechanical properties such that the M strength of the sintered body E-shaped form (E42/15) is high in average value and that no significant low-strength sample occurs, and is particularly suitable for use as a magnetic core of an electronic component for automobile mounting.

Claims

1. A granulated powder for MnZn-based ferrite, which is composed of an iron compound, a zinc compound, a manganese compound, a silicon compound, a calcium compound, a niobium compound and inevitable impurities,

When the total of the iron compound, the zinc compound and the manganese compound is 100 mol% in terms of _Fe2O3 , ZnO and _MnO , the iron compound is 51.5 to 56.8 mol% in terms of _Fe2O3 , the zinc compound is _5.0 to 15.5 mol% in terms of ZnO, and the manganese compound is the balance in terms of MnO,

The silicon compound is present in an amount of 50 to 300 ppm by mass in terms of _SiO2 , the calcium compound is present in an amount of 100 to 1300 ppm by mass in terms of CaO, and the niobium compound is present in an amount of 100 to 400 ppm by mass in terms of _Nb2O5 , relative to the total _amount of the iron compound, the zinc compound and the manganese compound.

The torque ratio of the MnZn ferrite granulated powder is 1.7 or more.

2. The granulated powder for MnZn-based ferrite according to claim 1, wherein

The MnZn ferrite granulated powder further contains at least one of a cobalt compound and a nickel compound.

The cobalt compound is contained in an amount of 3500 mass ppm or less in terms of CoO, and the nickel compound is contained in an amount of 15000 mass ppm or less in terms of NiO, relative to the total amount of the iron compound, the zinc compound, and the manganese compound.

3. A method for producing a granulated powder for MnZn-based ferrite, which is a method for producing the granulated powder for MnZn-based ferrite according to claim 1, the method comprising the following steps:

A pre-calcination step, pre-calcining a mixture of the iron compound, the zinc compound and the manganese compound to obtain a pre-calcined powder;

a mixing-crushing step of adding a silicon compound, a calcium compound and a niobium compound to the pre-calcined powder, mixing the mixture and then crushing the mixture to obtain crushed powder;

an immersion step of immersing the pulverized powder in an alkaline aqueous solution; and

In the granulation step, a binder is added to the pulverized powder after the impregnation step, the mixture is mixed, and then granulated to obtain granulated powder.

4. A method for producing a granulated powder for MnZn-based ferrite, which is a method for producing the granulated powder for MnZn-based ferrite according to claim 2, the method comprising the following steps:

a mixing-crushing step, in which a silicon compound, a calcium compound and a niobium compound are added to the pre-calcined powder, and at least one of a cobalt compound and a nickel compound is further added and mixed, and then crushed to obtain a crushed powder;

5. A MnZn ferrite, which is composed of a basic component, an auxiliary component and inevitable impurities,

When the total amount of iron, _zinc and manganese in terms of _Fe2O3 , ZnO and MnO is 100 mol%, iron in terms _of _Fe2O3 is 51.5-56.8 mol%, zinc in terms of ZnO is 5.0-15.5 mol%, and manganese in terms of MnO is the balance.

In the auxiliary components, SiO ₂ is 50 to 300 mass ppm, CaO is 100 to 1300 mass ppm, and Nb ₂ O ₅ is 100 to 400 mass ppm relative to the basic components.

The minimum value of the M strength measured for 100 samples of sintered bodies of type E42/15 conforming to JIS C2560-3-1:2006 exceeded 300 N, and the average value was 600 N or more.

6. The MnZn-based ferrite according to claim 5, wherein:

The auxiliary component further contains at least one of 3500 mass ppm or less of CoO and 15000 mass ppm or less of NiO relative to the basic component.

7. The MnZn-based ferrite according to claim 5 or 6, wherein:

The loss value of the MnZn ferrite at 100°C, 100kHz and 200mT is less than 380kW/ ^m3 .

8. A method for producing a MnZn ferrite, which is a method for producing the MnZn ferrite according to claim 5, the method comprising the following steps:

an immersion step of immersing the crushed powder in an alkaline aqueous solution;

A granulation step, in which a binder is added to the pulverized powder after the impregnation step, the mixture is mixed, and then granulated to obtain granulated powder; and

In the sintering step, the granulated powder is molded into a molded body, and then the molded body is sintered to obtain MnZn-based ferrite.

9. A method for producing a MnZn ferrite, which is a method for producing the MnZn ferrite according to claim 6, comprising the following steps: